Process for converting γ-butyrolactone into tetrahydrofuran

ABSTRACT

A process for converting γ-butyrolactone to tetrahydrofuran by treating the lactone with hydrogen in the presence of a cobalt-copper chromite catalyst at elevated pressures and temperatures.

This is a division of application Ser. No. 488,351, filed July 15, 1974and now U.S. Pat. No. 3,969,371.

BACKGROUND OF THE INVENTION

The invention relates to a process for converting γ-butyrolactone intotetrahydrofuran by treating the lactone with hydrogen in the presence ofa cobalt-copper chromite catalyst.

Various methods are known for the preparation of tetrahydrofuran as, forexample, dehydrating tetramethyleneglycol or hydrogenating furan. Morerecent methods involve hydrotreating a dicarboxylic acid or adicarboxylic acid anhydride and converting to tetrahydrofuran via theintermediate γ-butyrolactone Likewise, γ-butyrolactone can itself beused as the starting material. For example, in U.S. Pat. No. 3,370,067tetrahydrofuran is produced by the hydrogenolysis of butyrolactone inthe presence of a supported platinum metal catalyst or a transitionmetal catalyst where the metal has an atomic number from 21 to 30.However, the results obtained employing these catalytic materials wereunsatisfactory in that high conversions and high selectivity were notsimultaneously achieved.

It is an object of this invention to provide a process for convertingγ-butyrolactone to tetrahydrofuran in high yields.

Another object of this invention is to provide a selective process forconverting γ-butyrolactone to tetrahydrofuran.

Yet another object of this invention is to provide a new catalyst forconverting γ-butyrolactone to tetrahydrofuran.

Other objects and advantages will become apparent from a reading of thefollowing detailed description and examples.

DESCRIPTION OF THE INVENTION

Broadly, this invention contemplates a process for convertingγ-butyrolactone to tetrahydrofuran by treating the lactone with hydrogenin the presence of a cobalt-modified copper chromite catalyst.Generally, the process is conducted under elevated pressures andelevated temperatures. In one embodiment, conversion of γ-butyrolactoneis undertaken in the presence of a cobalt-modified copper chromitecatalyst under conversion temperatures ranging from about 100° to 350°C., preferably from about 250° to 300° C., and under pressures suitablyin the range of from about 100 to 400 kg/cm², preferably 150 to 200kg/cm².

The novel cobalt-modified copper chromite catalyst employed in theaforementioned process comprises CoO, CuO, Cr₂ O₃ and aluminum oxide. Ingeneral, the catalyst comprises from about 5.0 to 25.0, preferably 12.0to 14.5, weight percent CoO, from about 5.0 to 30.0, preferably 12.5 to16.0 weight percent CuO, from about 10.0 to 35.0, preferably 15.5 to19.5 weight percent Cr₂ O₃ and the balance aluminum oxide, for exampleeta or gamma alumina. The catalyst is employed in the process in amountsranging from about 1:100 to 1:1 parts by weight of catalyst per weightof γ-butyrolactone. A highly satisfactory weight ratio is 0.5 to 1.5,particularly 1 part, by weight of the catalyst per 5 parts by weight ofγ-butyrolactone. In a preferred embodiment of the invention, thereaction is carried out within 3 hours, at a temperature of 300° C. andunder a pressure of 150 kg/cm.sup. 2.

The cobalt-modified copper chromite catalyst of the invention isprepared by adding to aluminum hydroxide a salt of cobalt and of copper,eg. nitrate, chloride or an organic salt, such as the acetate, and CrO₃in an aqueous medium. After mixing and kneading the materials, therecovered mass is dried. The catalyst, after being ground and sieved iscalcined for about 1 to 5 hours at from about 250° to 500° C., suitablyat 450° C. in an inert gaseous environment such as argon, neon, heliumand preferably in a stream of nitrogen. Subsequently, the catalyst isactivated in a reducing environment, preferably in a stream of hydrogen,for 1 to 10 hours at about 200° to 300° C., preferably at 200° to 250°C. The so prepared catalyst is not pyrophoric nor does it lose itsactivity upon exposure to air. Moreover, it has a long catalyst life andis easily regenerated by heating with air at a temperature of from 200°to 500° C. and reducing with hydrogen at 150° to 450° C.

It was unexpectedly found that the instant cobalt-modified catalystproved to be superior in conversion and selectivity for the reduction ofγ-butyrolactone to tetrahydrofuran inasmuch as nickel catalysts hadpreviously been considered as equivalent reaction catalysts. It has nowbeen found that employing the cobalt-modified copper chromite catalystof our invention permits high conversion at high selectivities totetrahydrofuran from γ-butyrolactone, whereas correspondingnickel-modified catalysts are substantially less selective and producesubstantially more by-products.

The process of our invention is operated in the liquid phase, which is aconsiderable advantage over operating in the gaseous phase as far asconversion and reactor dimensions are concerned. The starting material,γ-butyrolactone is a well known material that can be provided by any ofthe methods heretofore taught by the art. In general, we employ thestarting material in undiluted condition in our process. However,reaction diluents such as gaseous diluents, e.g., nitrogen, argon ormethane, or liquid diluents such as hydrocarbons e.g., octane orcyclohexane, can be employed. However, there is no advantage to the useof diluents. Following the reaction, tetrahydrofuran is recovered byconventional means.

The product of our process, namely tetrahydrofuran represents a valuablematerial, particularly as a solvent or as a medium in a plurality ofreactions. It is also useful in the manufacture of polytetramethyleneglycol which in turn is used in the manufacture of synthetic fibers.

In order to more fully illustrate the nature of our invention and themanner of practicing the same, the following examples are presented. Inthese examples, the best mode contemplated by us for carrying out ourinvention is set forth.

EXAMPLE I

A cobalt-copper chromite catalyst according to the invention wasprepared as follows. Aluminum-tri-secondary butylate (232 grams) washydrolyzed with demineralized water and the formed alcohol was stripped.The aluminum hydroxide paste which had been concentrated to a volume of200 ml. was admixed with a solution of 38.9 grams of Cu(NO₃)₂.3H₂ O in35 ml. of water, 20.7 grams of CrO₃ in 20 ml. of water, 46.1 grams ofCo(NO₃)₂.6H₂ O in 50 ml. of water and the mass was kneaded for one hour.The paste like product was dried at 110° to 120° C. for one day,thereafter ground, sieved and calcined for 3 hours at 450° C., in astream of nitrogen. After cooling to 200° C. the stream of hydrogen wasintroduced at a flow rate of 33 liters per hour and the temperatureraised to 250° C. within 1 hour. The activation was completed after 2hours of hydrogen treatment. The so produced catalyst was not pyrophoricnor did it lose its activity upon exposure to air. The catalyst had thefollowing composition in weight percent: 14.6 -- CuO, 17.9 -- Cr₂ O₃,13.5 -- CoO and 54.0 -- Al₂ O₃.

Tetrahydrofuran was prepared from γ-butyrolactone as follows. A 2-literautoclave equipped with stirring means was charged with 250 grams ofγ-butyrolactone and 50 grams of the above-mentioned catalyst and thecharge was hydrogenated at 150 kg/cm² for four hours at about 300° C.The composition of the product was determined by gas chromatography andthe results are set forth in the Table below.

EXAMPLE II

A nickel-copper chromite catalyst was prepared according to theprocedure of Example I except that a solution of 47.2 grams ofNi(NO₃)₂.6H₂ O in 50 ml. of water was employed in place of the cobaltnitrate solution. The catalyst had the following composition in weightpercent: 14.6 -- CuO, 17.9 -- Cr₂ O₃, 13.5 -- NiO and 54.0 -- Al₂ O₃.

Tetrahydrofuran was prepared from γ-butyrolactone according to theprocedure of Example I except that the nickel-copper chromite catalystprepared above was employed. The composition of the product obtained wasdetermined by gas chromatography and the results are set forth in theTable below.

EXAMPLE III

Another cobalt-copper chromite catalyst according to this invention wasprepared as follows. An aluminum hydroxide paste was prepared from 249.5grams of aluminum-tri-secondary butylate as in Example I and mixed withsolutions of 20.7 grams of CrO₃ in 20 ml. of water, 24.9 grams ofCu(NO₃)₂.3H₂ O in 25 ml. of water and 46.1 grams of Co(NO₃)₂.6H₂ O in 40ml. of water and the mass was kneaded for one hour. As described inExample I, the mass was dried, calcined and activated. The catalyst hadthe following composition in weight percent: 13.9 -- CuO, 17.0 -- Cr₂O₃, 13.1 -- CoO and 56.0 -- Al₂ O₃.

Hydrotreatment of γ-butyrolactone was undertaken in the presence of thecatalyst prepared above according to the procedure of Example I exceptthat hydrogenation was conducted for three hours at a pressure of 200kg/cm². The composition of the product was determined by gaschromatography and the results are summarized in the Table below.

EXAMPLE IV

A nickel-copper chromite catalyst was prepared according to thefollowing procedure. An aluminum oxide paste obtained from 235.5 gramsof aluminum-tri-secondary butylate was mixed with the solutions of 44.7grams of Cu(NO₃)₂.3H₂ O in 45 ml. of water, 27.6 grams of CrO₃ in 25 ml.of water and 61.5 grams of Ni(NO₃)₂.6H₂ O in 65 ml. of water and themass was kneaded, dried, calcined and activated as described in ExampleI. The composition of the catalyst as weight percent was as follows:14.6 -- CuO, 21.0 -- Cr₂ O₃, 15.8 -- NiO and 48.6 -- Al₂ O₃.

Hydrotreatment of γ-butyrolactone was undertaken in the presence of thecatalyst prepared above in accordance with the procedure of Example III.The composition of the product was determined by gas chromatography andthe results are summarized in the Table below.

EXAMPLE V

Another cobalt-copper chromate catalyst was prepared according to theprocedure of Example I except that activation with hydrogen wasundertaken for 2 hours at 200° C.

Tetrahydrofuran was prepared from γ-butyrolactone in the presence of thecatalyst prepared above. The procedure of Example I was followed exceptthat the charge was hydrogenated for 4.5 hours at a pressure of 200kg/cm². The results are summarized in the Table below.

                                      TABLE                                       __________________________________________________________________________    Mole %                       Conversion                                       Example                                                                            THF NPA                                                                              NBA                                                                              PSE                                                                              BSE                                                                              GBL Other                                                                             mole-%                                                                              Selectivity                                __________________________________________________________________________     I   86.9                                                                              1.3                                                                              5.1                                                                              -- -- 0.6 6.9 99.4  87.5                                       II   66.5                                                                              7.7                                                                              5.0                                                                              -- -- 6.7 14.1                                                                              93.3  71.2                                       III  85.9                                                                              0.6                                                                              3.2                                                                              -- 0.6                                                                              3.6 6.0 96.4  89.2                                       IV   65.6                                                                              6.3                                                                              3.2                                                                              1.8                                                                              1.2                                                                              15.9                                                                              6.1 84.1  78.0                                        V   89.7                                                                              0.9                                                                              5.9                                                                              0.4                                                                              0.2                                                                              1.3 1.7 98.7  90.8                                       __________________________________________________________________________    Meaning of abbreviations                                                                   THF  Tetrahydrofuran                                                          NPA  n-Propanol                                                               NBA  n-Butanol                                                                PSE  Propionic Acid                                                           BSE  Butyric Acid                                                             GBL  γ-Butyrolactone                                                    (Other)                                                                            Ester, Butandiol-1,4                                        __________________________________________________________________________

The foregoing examples show clearly the superior effectiveness of thecobalt-modified copper chromate catalyst of our invention.

In the examples, the hydrotreatment was carried out at temperatures inthe range of from 290° to 300° C. Substantially higher temperatures,that is above 350° C. should be avoided. While pressures preferably inthe range of between 150 and 200 kg/cm² are employed, higher or lowerpressures can be used without substantially influencing the results.Depending on pressure, amount of catalyst charged and reactor volume,the reaction is completed within 3 to 6 hours. The catalyst addition maybe varied within wide limits. Preferably, catalyst is added in an amountof 1 part by weight per 5 parts by weight of γ-butyrolactone. It is alsopossible to use 0.5 part by weight of catalyst, however, thehydrotreating period must then be correspondingly extended. Higheramounts of catalyst do not have any adverse effects, but areuneconomical.

We claim:
 1. A catalyst suitable for the high conversion ofγ-butyrolactone selectively to tetrahydrofuran consisting essentially ofcobalt-modified copper chromite on aluminum oxide, wherein said catalystcomprises from about 12.0 to 14.5 weight percent CoO, from about 12.5 to16.0 weight percent CuO, from about 15.5 to 19.5 weight percent Cr₂ O₃and the balance aluminum oxide.
 2. A catalyst according to claim 1wherein said catalyst is calcined in an inert gas at about 200° to 500°C. and thereafter activated under reducing conditions at 200° to 300° C.3. A catalyst according to claim 1 wherein said catalyst is calcined atabout 450° C. in a stream of nitrogen and thereafter activated in astream of hydrogen at 200° to 250° C.